1. Field
Embodiments described herein relate to an organic electroluminescence display device using organic electroluminescence elements.
2. Description of the Related Art
An electroluminescence element is a self-emitting type display element, and has a wide viewing angle, excellent contrast, and excellent response time. The electroluminescence element is classified into an organic electroluminescence element and an inorganic electroluminescence element based on a material forming a light emitting layer therein. As compared to the inorganic electroluminescence element, the organic electroluminescence element has excellent brightness, driving voltage, and response speed characteristics. Also, the organic electroluminescence element is capable of expressing many colors.
In the organic electroluminescence element, typically, an anode electrode is formed on a substrate, and a hole transport layer HTL, a light emitting layer EML, an electron transport layer ETL, and a cathode electrode are sequentially stacked on the anode electrode. For example, the hole transport layer HTL, the light emitting layer EML, and the electron transport layer ETL may be organic thin films formed of an organic compound.
When voltage is applied between the anode electrode and the cathode electrode of the organic electroluminescence element, holes injected from the anode electrode migrate into the light emitting layer EML through the hole transport layer HTL. Similarly, electrons migrate into the light emitting layer EML through the electron transport layer ETL from the cathode electrode. Afterwards, excitons are generated by recombination of holes and electrons in the light emitting layer EML. The excitons transition from an excited state to a ground state, so that fluorescent molecules of the light emitting layer EML emit light. As light emission can selectively occur in every pixel, an image is formed on a panel where organic electroluminescence elements are integrated.
In the organic electroluminescence element, a micro cavity structure is utilized to improve both color stability of a light emission color and contrast. The micro cavity structure is a structure for generating a micro cavity effect. With the micro cavity effect, light generated in the light emitting layer EML is iteratively reflected between the anode electrode and the cathode electrode, so that light of a corresponding peak wavelength resonates and is emphasized, and light getting out of the corresponding peak wavelength is attenuated. In between the anode electrode and the cathode electrode, a length of a light path of an organic medium is adjusted so as to correspond to a spectrum peak wavelength of each original color light of RGB. For example, a red color light is obtained using a thicker organic layer, and a blue color light is obtained using a thinner organic layer.